1. Technical Field
The present invention relates to technology for compensating for defective nozzles in a printer when printing.
2. Related Art
Inkjet printers have a printhead with numerous fine nozzles, and operate by discharging ink from the necessary nozzles according to the character, image, or other marking to be printed on the recording medium.
The nozzle diameter is extremely small, ranging from approximately 30 μm to 60 μm, and because of the manufacturing precision or the operating conditions of the printer, for example, nozzles can become clogged and unable to discharge ink. When such defective nozzles are present, ink cannot be deposited at specific places on the recording medium, and content cannot be printed as desired. This phenomenon is also referred to herein as “dropped nozzles” or “dropped dots.”
When dropped nozzles occur in the black ink nozzle group, which is used most frequently in both monochrome and color printing, text information and barcode information can be lost and the above problem is even worse.
Japan Patent No. 3157880 and Japan Patent No. 4083403 teach technology for producing black when defective black ink nozzles are detected and compensating for defective nozzles by discharging and mixing cyan, magenta, and yellow inks instead of the black ink that the black ink nozzles should discharge.
The amount of ink discharged from the printer nozzles is always the same in the printer described in Japan Patent No. 3157880. In other words, there is only one size of dot that can be formed by the ink ejected from each of the color nozzles. When compensating for defective nozzles with this configuration, each black dot that is normally formed using only black ink is formed using three times as much ink because of the use of cyan ink, magenta ink, and yellow ink, and the size of the dot is thus inevitably larger. While dropped dots can be avoided, the problem of not being able to print as desired cannot be avoided. In addition, when the recording medium is paper, the ink can run or bleed through where compensation is applied, and delayed drying can result in the printout becoming smeared.
Japan Patent No. 4083403 teaches a printer that can discharge different amounts from ink from the same nozzle, but is silent regarding the relationship between the amount of black ink and the amounts of other inks when compensating for deficient discharge from the black ink nozzles by forming dots by mixing cyan ink, magenta ink, and yellow ink.